I recently had my transmission rebuilt, and I never really noticed this problem before. I have a 2001 f150 5.4l and whenever I accelerate to around 4,000 rpm or above (passing cars) I have no power at all. My rpms will continue to increase but I gain speed very very slowly. Most times I have to let off and let speed just gradually increase. It also seems that when it is around the 4000 rpm it doesnt want to shift and just stays wrapped up. Any solutions?

 

I would take it back to whoever "rebuilt" the trans. Sounds like the problem is with that and not the engine.